Many safety-related casualties and mishaps are caused by persons falling asleep while performing various tasks. For example, a large number of automobile accidents are caused by persons falling asleep while driving. A need therefor exists for a safety system that accurately monitors the vigilance (alertness) of a person and provides a warning to awaken that person at an early stage of vigilance loss.
The need for such a system has been recognized as numerous attempts have been made at designing an effective vigilance detection and warning system. None of the vigilance detection systems to date, however, accurately detects vigilance loss at a sufficiently early stage thereof to prevent safety-related casualties. The systems also suffer from other less serious drawbacks.
U.S. Pat. Nos. 3,863,243 (Skolnick et al.), 4,144,531 (Anbergen) and 4,953,111 (Yamamoto et al.) disclose prior art vigilance detection systems that employ an optical/electrical circuit for detecting eyelid movement. All of the disclosed systems optically monitor the frequency of complete eyelid closures or blinks; the Skolnick and Yamamoto systems do so directly while the Anbergen system does so indirectly by detecting eyelash movements. The disclosed systems are ineffective at providing a warning signal at an early stage of vigilance loss because the systems provide a warning signal only after a predefined threshold time period without a blink, which typically occurs at a relatively late stage of vigilance loss. In addition, such systems require the subject to wear glasses or goggles to carry the delicate optical circuitry. If the glasses or goggles are not precisely placed on the subject, then faulty operation may result.
Another prior art system includes a light-weight plastic head-piece that is placed on the head of a subject being monitored and provides an audio alarm signal to awaken the subject in response to significant radial head movements from a predefined alert state orientation, such as head nods. The head-piece system also is ineffective at warning the subject at an early stage of vigilance loss because head nods typically occur at a relatively late stage of vigilance loss. The head-piece system suffers from the additional drawback that voluntary radial head movements can falsely trigger the device to provide an alarm signal.
A further prior art system, described in U.S. Pat. No. 4,359,724 (Zimmerman), monitors the frequency of significant eyelid movements (i.e., blinks) of a subject. The Zimmerman system includes EMG electrodes that are placed on the eyelids of a subject and produce an electric signal in response to each significant eyelid movement. Analog circuitry, electrically connected to the sensors, includes a timer that is reset each time an electric signal is received. If the timer is not reset within a certain time period, then an audio alarm signal is provided to awaken the subject. Like the prior art optical systems, the Zimmerman system similarly monitors the frequency of blinks and therefore also is incapable of alarming a subject at an early stage of vigilance loss. The Zimmerman system additionally suffers from the drawbacks that EMG sensors are bulky and cumbersome and require precise placement for accurate operation.
Accordingly, a general object of the present invention is to provide a simple yet accurate system and method for monitoring the vigilance of a subject that detects vigilance loss at an early stage thereof.